JP2748951B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which the alignment state of liquid crystal is different for each minute area.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a liquid crystal panel in which liquid crystal is inserted between a pair of opposed transparent substrates. A common electrode and an alignment film are provided on the inner surface of one glass substrate,
A pixel electrode and an alignment film are provided on the inner surface of the other substrate. Recently, active matrix circuits are often formed together with pixel electrodes on the latter substrate. Further, a polarizing plate is provided outside each of these substrates.

In a liquid crystal display panel, liquid crystal molecules are aligned and pretilted according to the rubbing direction of the alignment films on both substrates. In a twisted nematic liquid crystal display device in which polarizing plates are arranged orthogonally, the rubbing directions of the alignment films on both substrates are almost perpendicular to each other, and the molecules of the liquid crystal form a spiral from one substrate to the other substrate. Twist.
Then, when no voltage is applied to the liquid crystal, the molecules of the liquid crystal maintain the initial twist and pretilt,
The incident light turns while traveling along the twist of the liquid crystal, and exits from the liquid crystal cell. At this time, a white display is obtained in the normally white mode in which the polarizing plates are orthogonally arranged. When a voltage is applied, the liquid crystal rises, the birefringence effect of the liquid crystal is weakened, the above-described light swirling effect is weakened, and the incident light is hardly transmitted through the liquid crystal cell, so that a black display can be obtained. In this way, an image having a bright and dark contrast as a whole is formed while controlling the voltage applied to the liquid crystal.

In the liquid crystal display device, the contrast of light and dark of an image changes depending on the direction in which a viewer views the screen. This is generally recognized as a viewing angle characteristic of a liquid crystal display device. For example, FIG. 9 is a diagram illustrating viewing angle characteristics of a liquid crystal display device. An alternate long and short dash line C is a voltage-transmittance curve when the vertically arranged liquid crystal display device is viewed from the front. Dashed line L,
U is a voltage-transmittance curve when viewed from obliquely above and obliquely below an angle of 40 degrees. In the case of the broken line L, even if the voltage is increased, the transmittance does not decrease much, so that even if an attempt is made to obtain a black display, the display becomes relatively bright. Broken line U
In this case, when a small voltage is applied, the transmittance is greatly reduced, and an image having a large contrast ratio is obtained. This is called a good viewing angle direction, and is indicated by a thick arrow in the following description. However, in the case of the broken line U, the transmittance increases again with an increase in the voltage, the correspondence between the voltage and the transmittance is inverted, and it may be inconvenient to obtain an intermediate color between white and black.

In order to solve the influence of the viewing angle characteristic, Japanese Patent Application Laid-Open No. 54-5754 and Japanese Patent Application Laid-Open
Japanese Patent No. 6624 proposes forming two regions having different alignment directions of liquid crystal molecules in one pixel. According to these proposals, by mixing a region having a certain viewing angle characteristic and a region having another different viewing angle characteristic, it is possible to improve the viewing angle characteristic as a whole.

FIG. 8 is a view showing an alignment process of such a conventional liquid crystal display device. FIG. 6 shows an area for one pixel, for example, which has two regions A and B in which the alignment state of the molecules of the liquid crystal is different. Light enters one of the substrates (here, the substrate on the light incident side is referred to as a lower substrate), passes through the liquid crystal, and exits from the other substrate (upper substrate). The rubbing direction of the alignment film on the lower substrate is indicated by an arrow 22a, and the rubbing direction of the alignment film on the upper substrate is indicated by an arrow 26a.

In a region A of FIG. 8, the rubbing direction 22a of the alignment film on the lower substrate is 45 degrees upward to the left, and the rubbing direction 26a of the alignment film on the upper substrate is 45 degrees downward to the left. The viewing angle characteristics in the case of such an alignment process match those shown in FIG. 9, and the direction of the good viewing angle indicated by the thick arrow is the upper side in FIG. On the other hand, in the region B, the rubbing direction 22a of the alignment film of the lower substrate is 45 degrees to the right and the rubbing direction 26a of the alignment film of the upper substrate is 45 degrees to the right. The viewing angle characteristics in the case of such an alignment process are upside down from those shown in FIG. 9, and the good viewing angle direction indicated by the thick arrow is on the lower side in FIG. 8.

When the region A and the region B are arranged adjacent to each other, the characteristic shown by the solid line I in FIG. 9 is obtained. The characteristic of the solid line I is obtained by adding the characteristics of the dashed line L and the dashed line U and dividing by 2, and is close to the characteristic of the dashed line C viewed from the normal direction.
The viewing angle direction with extremely high transmittance and the viewing angle direction with extremely low transmittance are eliminated, and the viewing angle characteristics are improved. The region A and the region B are provided for each minute region corresponding to the area of one pixel or several times or reciprocal times the area of one pixel.

[0009]

However, in order to obtain a liquid crystal display device having a region A and a region B as shown in FIG. 8, rubbing is performed by dividing the alignment film of each substrate into minute regions. It is necessary to. For example, in FIG. 8, the rubbing directions 22a and 26a of the area A are opposite to the rubbing directions 22a and 26a of the adjacent area B.

In order to perform such rubbing, it has been considered to perform rubbing using a mask having openings respectively corresponding to minute regions A and B, and a resist is used as a mask. In this case, first, an alignment film is applied to the substrate, a resist is applied on the alignment film, and an opening corresponding to the region A (or B) is provided in the resist by photolithography. Rubbing is performed in a predetermined direction. Next, the resist is removed by etching, another resist is applied on the alignment film, and an opening corresponding to the region B is provided in the resist by photolithography. Perform rubbing. Next, the resist is removed by etching.

As described above, there is a problem that performing the alignment treatment so that the alignment state of the liquid crystal is different for each minute region requires many steps as described above. In addition, conventionally, the rubbed portion was initially disturbed by subsequent rubbing or etching or changed with time, and the alignment performance of the liquid crystal was sometimes reduced. SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device capable of easily and reliably performing an alignment process in which the alignment state of liquid crystal is different for each minute region.

[0012]

A liquid crystal display device according to the present invention comprises first and second opposed substrates 16 and 18, an electrode 21 and an alignment film 22 provided on the inner surface of the first substrate.
And an electrode 24 and an alignment film 26 provided on the inner surface of the second substrate, and a liquid crystal 20 inserted between the first and second substrates. In a liquid crystal display device in which the alignment film 22 of the first substrate and the alignment film 26 of the second substrate are aligned in a minute area, the alignment film 22 of the first substrate and the alignment film 22 of the first substrate are different. The adhesion of the second substrate to the lower layer structure of the alignment film 26 is changed for each of the minute regions, and the pretilt of the liquid crystal is changed for each of the minute regions.

[0013]

In the above structure, the adhesion between the alignment film 22 of the first substrate and the alignment film 26 of the second substrate is changed for each of the minute regions, and the pretilt of the liquid crystal is changed for each of the minute regions. Are different. Therefore, on one substrate, a first pretilt is obtained in a certain minute area, and a different second pretilt is obtained in an adjacent minute area. In this case, the rubbing directions of the alignment films on one substrate may be the same. On the other substrate, a second pretilt is obtained in a minute region facing a certain minute region of the one substrate, and a first pretilt is obtained in a minute region adjacent thereto. Also in this case, the rubbing directions of the two minute regions may be the same. Thus, both substrates can form a liquid crystal display device having two minute regions having different liquid crystal alignment states by one rubbing.

[0014]

FIG. 1 shows a liquid crystal panel 10 of a liquid crystal display device according to an embodiment of the present invention. On both sides of the liquid crystal panel 10, a polarizing plate (not shown) has a vertical relationship when in a normally white mode. Or in a parallel relationship in the normally black mode. The liquid crystal panel 10 has a liquid crystal 20 sealed between a pair of transparent glass substrates 16 and 18. The liquid crystal 20 uses a twisted nematic liquid crystal. Light from a light source (not shown) enters the liquid crystal panel 10 from, for example, the direction of arrow L, and a viewer views the liquid crystal panel 10 from a direction opposite to the incident direction. The substrate 16 is referred to as a lower substrate, and the substrate 18 on the viewer side is referred to as an upper substrate.

The color filter layer 1 is formed on the inner surface of the lower substrate 16.
9, an ITO common electrode 21 and an alignment film 22 are provided,
A pixel electrode 24 and an alignment film 26 are provided on the inner surface of the upper substrate 18. The pixel electrode 24 provided on the upper substrate 18 is connected to an active matrix circuit. As shown in FIG. 5, the active matrix circuit includes a data bus line 30 and a gate bus line 32 extending vertically and horizontally in a matrix, and the pixel electrode 24 includes a thin film transistor (TF).
T) 34 to the data bus line 30 and the gate bus line 32. FIG. 6 shows a color filter layer 19 of the lower substrate 16, which is a color filter (R, G, B) 19a provided corresponding to the pixel electrode 24, and a black matrix 19 for opening the color filter 19a.
b.

As shown in FIG. 1, the alignment state of the liquid crystal 20 is different for each of the minute regions A and B. For this reason, the alignment film 22 of the lower substrate 16 and the alignment film of the upper substrate 18 are different. Reference numeral 26 designates an alignment process for each area corresponding to the minute regions A and B. In the region A, the liquid crystal molecules near the alignment film 22 of the lower substrate 16 have a pretilt α ₂ , and the liquid crystal molecules near the alignment film 26 of the upper substrate 18 have a pretilt α ₁ . Conversely, this area A
In the region B adjacent to the alignment film 22 of the lower substrate 16,
Liquid crystal molecules pretilt alpha ₁ next to the vicinity of the upper substrate 18
The liquid crystal molecules in the vicinity of the alignment film 26 are pretilt α ₂ . Here, there is a relationship of α ₁ > α ₂ .

Therefore, the alignment film 22 of the lower substrate 16 is made of a liquid crystal.
The molecules alternate in angle α₁, Α_TwoTo pretilt with
The orientation film 26 of the upper substrate 18 is also
Crystal molecules alternately at an angle α₁, Α_TwoTo pretilt with
It is oriented. In the present invention, the alignment film of the lower substrate 16 is used.
22 and the alignment process of the alignment film 26 of the upper substrate 18
The alignment film 22 of the lower substrate 16 and the upper substrate
The adhesion of the alignment film 26 to the lower layer structure of the alignment film 18 is in the region A,
It is changed every B. That is, any of the alignment films 22 and 2
6 also has a large pretilt α₁In areas where you get
Wearability P ₁Is small and the small pretilt α_Two
In the area where_TwoShould be small. This
Where P₁> P_TwoThere is a relationship.

FIG. 5 and FIG. 6 show setting examples of minute regions A and B having different alignment states of the liquid crystal. The minute regions A and B having different alignment states of the liquid crystal are separated by a line passing substantially through the center of the pixel electrode 24 (and the color filter (R, G, B) 19a) and a line passing through the gate bus line. Alternatively, the minute regions A and B can be divided by a line parallel to the data bus line 30. Region A in pretilt alpha ₁ next to FIG. 5, corresponding to the pretilt alpha ₂ in the area A in FIG. 6 with this. The same applies to the area A.

FIG. 1 shows that liquid crystal molecules are twisted. In the minute region A, the molecules of the liquid crystal in contact with the alignment film 26 have an alignment direction from the back left to the front right and are pretilted at an angle α ₁ . In the minute area B, the molecules of the liquid crystal in contact with the alignment film 26 have an alignment direction from the back left to the front right and are pretilted at an angle α ₂ . That is, in the upper substrate 18, in both of the minute regions A and B, the molecules of the liquid crystal in contact with the alignment film 26 have the alignment direction from the back left to the front right, but the pretilt angles α ₁ and α
_Two are different. This relationship is based on the alignment film 22 of the lower substrate 16.
The same applies to the above, and although the molecules of the liquid crystal in contact with the alignment film 22 are in the alignment direction from the right rear to the left front, the pretilt angles α ₁ and α ₂ are different.

That is, the adhesiveness P ₁ , P 2 to the lower layer structure of the alignment film 22 of the lower substrate 16 and the alignment film 26 of the upper substrate 18.
₂ is different for each of the regions A and B, the respective alignment films 2
The rubbing of the liquid crystal 2 and 26 is performed only in a certain direction.
The orientation state of 0 is different for each of the minute regions A and B.

FIG. 2 is a view showing a process of forming the alignment film 26 on the upper substrate 18. The alignment film 22 of the lower substrate 16 can be formed in a similar process. As shown in FIG.
An adhesion improving agent such as a silane coupling agent is provided on the pixel electrode 24 and the gate bus line 30 by patterning in an area corresponding to the minute regions A and B. The patterning of the adhesion improving agent is performed by applying a adhesion improving agent over the entire surface, forming a resist, and performing a lift-off process.

Next, as shown in FIG.
2 and 26 are applied. The alignment films 22 and 26 have an imidization ratio of 1
It is composed of 00% of an organic alignment agent such as polyimide. Next, as shown in (C), the alignment films 22 and 26 are formed.
Rubbing in a certain direction. The rubbing is performed by rotating a rubbing roller 57 around which a rubbing material such as fiber is wound on the alignment film 26 of the upper substrate 16 while rotating the rubbing roller 57 in the direction of the arrow.

The alignment films 22 and 26 thus formed
Of the silane coupling agent (SC) as an adhesion improving agent and a portion without the silane coupling agent (SC) were measured in a liquid crystal display device using the same. Two samples were used for the alignment film. Sample 1 was JALS-2 manufactured by Japan Synthetic Rubber.
19 and sample 2 is also JALS-249. The results of the pretilt angle were as follows (unit: degree).

[0024] From this, it was found that when an adhesion improving agent such as a silane coupling agent was used, the alignment films 22 and 26 thereon were strongly adhered to the lower layer structure, and as a result, the pretilt angle of the liquid crystal was increased. Therefore, if the adhesion improver is patterned, minute regions A and B in which the alignment state of the liquid crystal 20 is different can be obtained by one rubbing. In addition, other than the silane coupling agent can be used as the adhesion improver.

FIG. 3 is a diagram showing an example in which an ozone asher is used as means for making the adhesion between the alignment films 22 and 26 different. 4A, a resist 4 is formed on the pixel electrode 24 and the gate bus line 30 on the upper substrate 18.
2 is formed by patterning, and ozone is sprayed using this as a mask. As shown in FIG.
When 2 is removed, only the portion where no resist 42 is present is subjected to surface treatment. Then, as shown in (C), the alignment films 22 and 26 are applied. Alignment films 22, 26
Is composed of an organic alignment agent such as polyimide having an imidization ratio of 100%. Next, as shown in (C), the alignment films 22 and 26 are rubbed in a certain direction using a rubbing roller 57.

The alignment films 22, 26 formed in this way
The pretilt angle was measured at the part where the adhesion was increased by the ozone asher treatment (OA) and the part where the adhesion was not changed and the original adhesion was maintained in the liquid crystal display device using. The same two samples as described above were used for the alignment film. The results of the pretilt angle were as follows (unit: degree).

[0027] From this, it was found that the surface treatment with an ozone asher or the like strongly adhered the alignment films 22 and 26 to the lower layer structure, thereby increasing the pretilt angle of the liquid crystal.

Further, as shown in FIG. 4, there is a correspondence between the ozone asher processing time and the resulting pretilt angle, and by appropriately controlling the ozone asher processing time, the ozone asher processing time is close to a desired value. It can be a pretilt angle. The surface treatment is not limited to the ozone asher, but may be performed by other surface treatments such as an oxygen plasma treatment.

FIG. 7 is a diagram simply showing the orientation processing described above. As can be seen from the above description, in the minute region A, the rubbing direction of the alignment film 26 of the upper substrate 18 is indicated by an arrow 26a, and the rubbing direction of the alignment film 22 of the lower substrate 16 is indicated by an arrow 22a. In the minute region A, the liquid crystal molecules in the vicinity of the alignment film 26 of the upper substrate 18 pretilt at a large angle α ₁ , and the lower substrate 1 opposed thereto is tilted.
The liquid crystal molecules near the alignment film 22 of No. 6 pretilt at a small angle α ₂ . In the minute region B, the molecules of the liquid crystal near the alignment film 26 of the upper substrate 18 have a large angle α.
Pretilted _2, pretilt molecules of the liquid crystal at a small angle alpha ₂ in the vicinity of the alignment film 22 of the lower substrate 16 which faces.

As described above, in the minute regions A and B,
One of the substrates 16 (1
8) pretilted at large angles alpha ₁ in side, if you pre-tilt at a small angle alpha ₂ in the other substrate 18 (16) side, when applying a voltage, the liquid crystal molecules in the middle portion by the arrows in FIG. 1 As shown, it rises in the direction with a large pretilt angle.

Therefore, in the small area A in FIG.
The rising of the liquid crystal follows the alignment processing of the alignment film 26 of the upper substrate 18 indicated by the arrow 26a. In the minute region B, the rise of the liquid crystal follows the alignment processing of the alignment film 22 of the lower substrate 16 indicated by the arrow 22a. Therefore, the rise of the liquid crystal in the minute area A in FIG. 7 is the same as that in the area A shown in FIG. This is because the rise of the liquid crystal in FIG. 8 also follows the arrow 26a. Similarly, the rise of the liquid crystal in the minute area B in FIG. 7 is the same as that in the area B shown in FIG.

However, the lower substrate 16 shown in FIG.
The arrow 22a indicating the rubbing direction of the alignment film 22 is directed in the opposite direction to the arrow 22a indicating the rubbing direction of the alignment film on the lower substrate 16 in the region A of FIG. Therefore, the lower substrate 16
In the vicinity, the molecules of the liquid crystal in FIG. 7 are oriented parallel to the molecules of the liquid crystal in FIG. 8, and the pretilt direction is reversed.
Therefore, the molecules of the liquid crystal in the minute region A in FIG. 7 are twisted similarly to the molecules of the liquid crystal in the region A in FIG. Small area B
The same applies to.

Since the pretilt of the liquid crystal molecules near the alignment film 26 of the upper substrate 18 is opposite to the pretilt of the liquid crystal molecules near the alignment film 22 of the lower substrate 16, the pretilt angle of the liquid crystal is changed by applying a voltage. When rising to the larger one, the behavior of the molecules of the liquid crystal with a small pretilt angle turned in the opposite direction seems to be unstable. Nevertheless, it has been confirmed that the liquid crystal display device according to the present invention can form a much clearer image than the liquid crystal display device formed as shown in FIG. The reason is that, in the present invention, rubbing needs to be performed only once near the end of the alignment process to form a plurality of alignment states. The lower substrate 16 and the lower substrate 18 can be assembled in a so-called hot state without any time from the rubbing operation, and the liquid crystal 20 can be immediately injected, so that the liquid crystal 20 can be sealed without a change over time in the rubbing process. I think that the. Further, according to the present invention, the rubbing process can be performed without disturbing the rubbing effect, as compared with the conventional case where exposure and etching are performed after the first rubbing is performed, and then the second rubbing is performed. Seems to be stable.

Further, for example, in the minute area A in FIG.
The rise of the liquid crystal mainly depends on the alignment treatment of the alignment film 26 of the upper substrate 18, and the effect of the alignment treatment of the alignment film 22 of the lower substrate 16 seems to be secondary. In that case, there may be a doubt that the alignment treatment of the alignment film 22 of the lower substrate 16 may not be performed at all. However, when only one substrate is oriented and the other substrate is not, the liquid crystal twists exactly 90 degrees unless the relationship between the liquid crystal material and the thickness of the liquid crystal layer is very strictly defined. do not become. In the present invention, the alignment treatment of the alignment film 22 of the lower substrate 16 assists in twisting the liquid crystal at least exactly 90 degrees in connection with the alignment treatment of the alignment film 26 of the upper substrate 18.

[0035]

As described above, according to the present invention,
An alignment process in which the alignment state of the liquid crystal differs for each minute region can be easily and reliably performed, and a liquid crystal display device having excellent viewing angle characteristics and contrast can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIGS. 2A and 2B are views showing the alignment treatment step of FIG. 1, wherein FIG. 2A shows the provision of an adhesion improver, FIG. 2B shows the provision of an alignment film, and FIG. FIG.

FIG. 3 is a view showing another example of the alignment treatment step in FIG. 1;
(A) shows that the surface treatment is performed, (B) shows that the resist is removed, (C) shows that the alignment film is provided, and (D) shows that the rubbing is performed.

FIG. 4 is a diagram showing a relationship between a surface treatment time and a pretilt angle.

FIG. 5 is a view showing an alignment process for one substrate.

FIG. 6 is a diagram illustrating an alignment process of the other substrate.

FIG. 7 is a diagram simply showing the alignment processing of FIG. 1;

FIG. 8 is a diagram simply showing a conventional alignment process.

FIG. 9 is a diagram illustrating viewing angle characteristics of a liquid crystal display device.

[Explanation of symbols]

 16, 18: substrate 20: liquid crystal 21, 24: electrode 22, 26: alignment film

Claims (3)

(57) [Claims] A first and a second opposing substrate (16, 1);
8) and an electrode (21) provided on an inner surface of the first substrate.
And an alignment film (22), an electrode (24) and an alignment film (26) provided on the inner surface of the second substrate, and the first and second films.
And an alignment film (22) of the first substrate and an alignment film (22) of the second substrate such that the alignment state of the liquid crystal is different for each minute region. In the liquid crystal display device in which 26) is subjected to an alignment treatment in a fine region, the adhesion of the alignment film (22) of the first substrate and the alignment film (26) of the second substrate to the lower layer structure is reduced. A liquid crystal display device, wherein the pretilt of the liquid crystal is changed for each minute region, and the pretilt of the liquid crystal is changed for each minute region. 2. An adhesion improving agent layer is provided below the alignment film (22) of the first substrate and the alignment film (26) of the second substrate, whereby the adhesion of the alignment film is changed. The liquid crystal display device according to claim 1, wherein: 3. A surface treatment is performed on a lower layer of the alignment film (22) of the first substrate and an alignment film (26) of the second substrate,
2. The liquid crystal display device according to claim 1, wherein the adhesiveness of the alignment film is changed thereby.